The present invention relates to a grinding method and a surface grinder for minutely grinding single or both surfaces of a workpiece, such as a thin-plate-like hard wafer to be used for a semiconductor, with extremely high accuracy.
In addition, the present invention relates to a workpiece support mechanism, and a work rest.
Further, the present invention also relates to a surface grinder having a contact preventing apparatus for preventing the workpiece supporting member from being contacted with a grinding wheel.
Conventionally, after having been sliced off from an ingot through use of an inner blade saw or wire saw, a wafer, such as a silicon wafer, is ground by a lapping machine.
The wafer sliced off from the ingot is rough in terms of surface roughness and accuracy of geometry. It takes very long time to lap the wafer sliced off from the ingot, resulting in deterioration of working efficiency. At the time of grinding of one surface of the wafer, another surface of the wafer is held by a vacuum chuck. For this reason, although the wafer sliced off from the ingot is plane in shape while being held, the wafer tends to become warped after removal of the workpiece from the vacuum chuck.
In a case where, with a view to improving the efficiency and accuracy of a lapping operation, an attempt is made to grind the wafer, a required degree of accuracy is obtained in a very short time. However, if the wafer is held by the vacuum chuck as a conventional matter, a required degree of accuracy cannot be obtained. This is a problem.
Conventional grinding method for a wafer is, however, known and described in, e.g., Japanese Utility Model No. 3028734; "Machines and Tools," July, 1996, pp. 60-64; and "Proceedings of Abrasive Engineering Society", July, 1995, vol. 3, No. 4, pp. 20-23.
Generally, a conventional double disc surface grinder comprises upper and lower rotary spindles rotatively arranged in alignment with each other. Grinding wheels (so called grindstone) are held and secured to the respective ends of the rotary spindles which are opposite to each other by upper and lower grinding wheel holders. The grinding wheels are positioned so as to be opposite to each other such that the grinding surfaces of the grinding wheels are arranged in parallel with each other. A workpiece hold mechanism for supporting a workpiece is provided between the grinding wheels so as to be movable, and a workpiece support plate is provided for the workpiece hold mechanism. While the workpiece is retained by the workpiece support plate, both grinding wheels are rotated and moved close to the workpiece. Both surfaces of the workpiece are ground so as to be parallel to each other by grinding surfaces of the grinding wheels. At that time, the surface grinder is operated in such a manner that the workpiece is only ground by the upper and lower grinding wheels without grinding of the workpiece support plate.
On the other hand, in many cases, the workpiece support plate becomes warped by its dead weight. At the time of grinding of the workpiece, it has been difficult to retain the workpiece support plate while being kept from contact with the grinding wheels.
It is conceivable that the workpiece support plate is stretched in the form of a very thin sheet. However, in such a case, it is difficult for the workpiece support sheet to stand the grinding torque exerted on the workpiece during a machining operation.